Within that ocean a species of brilliant fish evolved. Those fish were so intelligent that they took up physics, and formulated the laws that govern motion. At first they derived quite complicated laws, because the motion of bodies within water is complicated.
One day, however, a genius among fish, call her Fish Newton, had a startling new idea. She proposed fundamental laws of motion––Newton’s laws––that are simpler and more beautiful than the laws the fish had derived directly from experience. She demonstrated mathematically that you could reproduce the observed motions from the new, simpler laws, if you assume that there is a space-filling medium that complicates things. She called it Ocean.

This is the clearest statement I have seen (at least from a recognised scientist in the field) that “space” is full of matter, albeit a different form of matter to the one we are familiar with. It makes me wonder how much the underlying mental picture of what space consists of affects the interpretation of the observational evidence and the maths by different scientists. I suspect that it may be more than they would like to think.